COVID-19 unlikely to be transmitted through tears

The transmission of the coronavirus disease 2019 (COVID-19) through tears appears to be unlikely, according to a Singapore study.

“In this study, we attempted to determine the possibility of transmission through tears by assessing for the presence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) with viral isolation and quantitative reverse transcription polymerase chain reaction (RT-PCR),” the researchers said, adding that the risk of transmission through this route is low, though further mechanistic studies are needed for confirmation.

Both nasopharyngeal swab and tear samples were collected from 17 COVID-19 patients and sent for RT-PCR detection of the virus. Analyses were carried out in consideration of ocular symptoms caused by other coronaviruses, such as red eye, blurring of vision, discharge, tearing and colour desaturation. These, along with other clinical data, were obtained from the patients’ electronic health records.

Sixty-four samples were collected over the study period and none of which tested positive for SARS-CoV-2. Most of the samples were collected during the second and third week after symptom onset. [Ophthalmology 2020;doi:10.1016/j.ophtha.2020.03.026]

Similarly, none of the enrolled patients demonstrated any of the ocular symptoms that were under monitoring, though there was one case of conjunctival injection and chemosis, which arose during hospital admission. In contrast, all but three of the participants developed upper respiratory symptoms commonly associated with COVID-19, including cough, sore throat and rhinorrhoea.

Notably, the negative RT-PCR results for tear samples coincided with viral positivity as detected in the nasopharyngeal swabs, implying that despite active infection, shedding through the lacrimal ducts is unlikely. This was supported by the fact that only one patient developed ocular symptoms even if most had respiratory presentations.

“To our knowledge, this is the first study comparing viral shedding in tears with NP results during the course of COVID-19 infection,” the researchers said, pointing out that several limitations should be taken note of.

Among these was the use of different assays, performed in different laboratories, for tear and nasopharyngeal samples. The failure to take conjunctival tissue was also a methodological shortcoming, though it was opted for to avoid further distressing the patients. The small sample size and the difficulties in sampling during the early stages of the infection should also be taken into consideration.

“More studies are required to definitely prove the presence of [angiotensin-converting enzyme 2 receptors] on corneal and conjunctival cells. Future studies involving more patients with ocular symptoms should also be considered,” the researchers said.

“Finally, future studies should consider the association between serum viral load and viral shedding in tears,” they added. “Unfortunately, no blood samples were analysed for this experiment as they were not routine clinical investigation in the management of patients.”